1. Field of the Invention
The present invention relates to a lighting unit and a projection display apparatus, each including a red light imager modulating red component light, a green light imager modulating green component light, and a blue light imager modulating blue component light.
2. Description of the Related Art
Heretofore, a projection display apparatus has been known which includes: three light imagers corresponding to light of three colors (red component light, green component light, and blue component light); a cross dichroic cube combining light emitted from the three light imagers; and a projection unit projecting the light combined by the cross dichroic cube.
Here, consider a projection display apparatus using a light source which emits white light like a lamp in terms of the improvement of luminance and the improvement of color purity. As for the improvement of luminance, it is preferable (1) to widen a band of each color component light used in the projection display apparatus, and (2) to use a fourth color component (e.g., yellow component light) other than the red component light, the green component light, and the blue component light. Meanwhile, as for the improvement of color purity, it is preferable (1) to narrow a band of each color component light used in the projection display apparatus, and (2) not to use a fourth color component (e.g., yellow component light) other than the red component light, the green component light, and the blue component light. Therefore, there is a trade-off between the improvement of luminance and the improvement of color purity.
Under such circumstances, the following, for example, have been proposed: (1) a four-panel projection display apparatus provided with a light imager which modulates fourth color component light (for example, Japanese Patent Application 1), and (2) a projection display apparatus provided with a movable dichroic mirror which cuts off fourth color component light (for example, Japanese Unexamined Patent Application 2).
Moreover, it is also possible to design a projection display apparatus having a digital micromirror device (DMD) by providing a movable dichroic mirror thereto. In this case, the projection display apparatus can be configured to be switchable between a luminance improvement mode and a color purity improvement mode by use of the movable dichroic mirror. [Japanese Patent Application 1: Publication No. 2002-287247] [Japanese Unexamined Patent Application 2: Publication No. Hei 7-318883]
However, a four-panel projection display apparatus is not capable of combining light of four or more colors by using a single cross dichroic cube. Accordingly, the projection display apparatus needs to have two or more dichroic cubes (or cross dichroic cubes) and thereby to have a long back-focus of a projection unit.
Consequently, a projection unit used for the projection display apparatus using light of three colors cannot be used for the four-panel projection display apparatus, so that cost of the projection display apparatus as a whole increases.
Meanwhile, in a projection display apparatus provided with a movable dichroic mirror, a failure tends to occur because the dichroic mirror needs to be mechanically moved.